Generally, a permanent magnet motor is operated in a speed control mode or torque control mode and a method of controlling both speed and torque may be used depending on applications, and in the latter case, a variable magnetic flux permanent magnet motor in which magnetic flux of the permanent magnet is variable depending on operation modes is used.
In such a variable magnetic flux permanent magnet motor, magnetic flux of the motor is varied by magnetization or demagnetization. For example, in the case of a washing machine, which is a typical application of the variable magnetic flux permanent magnet motor, magnetic flux of the motor is varied by changing a magnetizing amount or demagnetizing amount of the permanent magnet because high-speed rotation and low torque are required for spin-drying laundry and low-speed rotation and high torque are required for washing laundry.
Meanwhile, a conventional permanent magnet motor mostly uses magnetization current control or demagnetization current control because controlling the magnetic flux itself to vary the magnetic flux for selectively controlling the speed or torque is very difficult.
However, since magnetic flux of a motor cannot be accurately controlled only by the control of magnetization current or demagnetization current, and particularly, the magnetization current and demagnetization current used for the control are initially set or have a fixed value, there is a problem in that control of a motor cannot adapt to environmental changes such as aging of the motor or the like.